


Doggy 101: Training Your New Puppy

by MeGaLoTrash



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, BDSM, Begging, Cuckolding, Ecto-Penis (Undertale), Ecto-Vagina (Undertale), Explicit Sexual Content, Honeyvenom, M/M, Master/Pet, Multi, Name-Calling, Oral Sex, Orgasm Delay/Denial, Overstimulation, Threesome - M/M/M, ecto-breasts, honeybbq, swapfellcest - Freeform
Language: English
Status: Completed
Published: 2018-02-05
Updated: 2018-02-05
Packaged: 2019-03-14 08:26:37
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,363
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13586190
Author URL: https://archiveofourown.org/users/MeGaLoTrash/pseuds/MeGaLoTrash
Summary: Stretch walked in on something he shouldn't have, but rather than being annoyed the Swapfell brothers want to get to know him a little betterForSapphire-Sphinx





	Doggy 101: Training Your New Puppy

Stretch tried not to give anything away to his 'captors'. But with the way Slim’s fingers were working slowly over his ribcage he knew that it was only a matter of time before he lost the ability to think clearly. When he had decided to pay a visit to his rougher looking double earlier that morning he didn’t anticipate that he would end up writhing against his far too skilled hands. But that surprise was nothing on the fact that they were doing this on Slim’s bed. With his brother watching them less than a foot away in a nearby chair. Black’s expression was calm, but his eye lights burned with such intensity that was leaving Stretch breathless. 

“You Like When He Touches You Like That, Hmm?” Black muttered in a voice unlike anything Stretch had ever heard coming from the other skeleton. 

In the rare occurrences he’d heard his brother’s darker copy speak when he wasn’t barking orders at Slim, it had been to trade loaded insults. Stretch hadn't even realised that their back and forth was becoming more and more sexually charged until it got to a point where he kept seeing Black's smug face when he was alone. Black's voice was still intimidating now, but it was dripping with desire. The low cadence sent shivers up Stretch’s spine. He knew he wouldn’t be able to resit much longer, but still he tried not to whimper when Black looked him up and down while licking his teeth. 

“Staying Silent Are We? I Know You Want More, I Can See It In Your Eyes.” Black teased as he leant forward from his vantage point “Just Say The Word And We Can Continue”

Stretch let out a shaky breath as Slim’s hands gravitated a little lower and brushed against his spine. Part of him really wanted this, to find out what they had planned for him, but everything had all happened so fast his mind was having a hard time catching up. He had come to this universe out of boredom, knowing that his alternate always had interesting ways of finding some questionable fun. What he hadn’t anticipated was walking in on Slim on his knees, blindfolded and tied up, with Black’s cock so far down his conjured throat that Stretch had choked on his words in sympathy. 

So many things had ran though his mind as he tried to make a speedy exit. He always kind of knew that Black and Slim were and item, but even though Black bossed his brother around he thought it was all for show. He would never had guessed that the terrifying version of himself that everyone knew not to fuck with would so willingly submit like that. Black’s face was stuck in his mind though. The captain of the royal guard had two expressions; stoic and angry. What Stretch had seen while Black was fucking his brother’s face was something else entirely. Just thinking about that lecherous expression had made his soul beat erratically. Stretch had been so distracted that he had only noticed an untied Slim had caught up with him when he felt himself being grabbed from behind. 

Slim had teleported them back to his home and pulled him onto the bed, insisting that his ‘lord’ wanted a quick word. Black was quick and to the point; he knew Stretch’s reaction hadn’t been one of disgust, and even though he had tried to protest Black was quick to point out that his magic was already glowing. He offered Stretch the opportunity to be with them, to experience pleasures he had only dreamed about, on the condition that he agreed to put his trust in Black completely. Black was already moving on to talking about a safe word and limits when Stretch had started to babble in protest. Black heard him out but had quickly seen through his flimsy excuses, instructing Slim to try and persuade him instead. 

That was how he had ended up in his current predicament; with Slim’s hot breath on his vertebrae as he tried not to fall apart under Black’s stare. It had only been about ten minutes of agonisingly slow touches, but since they were so similar Slim knew all of his sensitive spots. Stretch knew it wasn’t a question of if he was going to break, but when. His reluctances wasn’t because he didn’t want this though. It was no secret that Stretch found them both attractive; he’d often get a little too chummy with slim when they were drunk and he’d been caught staring at Black’s ass more times than he’d care to admit. But he’d never considered the possibility that either of them would be interested when they had each other. 

Stretch wanted them. But he was struggling to agree to something so far outside his comfort zone.

He knew Black had no intention of hurting him though. He may have been a smug asshole, and had alluded to wanting to ‘break’ him, but the guy knew what he was doing. Stretch had caught a glimpse of what the Black could offer earlier, and his soul was pounding inside his ribcage at the thought of getting to experience that himself. Slim was doing a very good job at persuading him; the touches along his spine were growing firmer, and he had shifted their positions so that his dripping tongue was inches from Stretch’s open mouth. Stretch felt his eye sockets flicker shut as he got lost in the moment, only to have Black stop his brother’s efforts with a snap of his fingers. 

“Not Yet Mutt, I Need To Hear Him Say It” Black ordered, making Slim draw back as he panted heavily. 

Stretch whined, missing his touch already. He knew he was playing a dangerous game, but in that moment he wanted them both so badly it hurt. “oh gods- i-i-i need this! please don’t stop- ah fuck!” 

Slim may have cut him off by finally tugging on his spine just right, but Black was quick to reprimand him for losing himself with a sharp smack of his crop against the inside of his femur. The worst thing was that Stretch’s yelp of pain sounded an awful lot more like a moan. 

“Lesson One, Watch Your Language.” Black brought the crop to rest just underneath Stretch’s chin tauntingly before flashing him a wicked grin. “Mutt, Strip Him And Get Him To Form Something Useful To Fuck” 

Slim didn’t mess around, bringing Stretch further into his lap while he removed every scrap of clothing. Stretch didn’t have time to worry about being self conscious before Slim pulled him into a bruising kiss and moved a hand between his legs. Stretch moaned into the kiss, the taste of cigarettes and sex on his double’s tongue making his head spin. The realisation he could be tasting Black’s magic as well was enough to make Stretch arch into Slim’s hand as he stimulated the magic swirling around his pelvis. Stretch would have been embarrassed about how quickly his magic morphed into a dripping slit if he wasn’t already addicted to how the other skeleton was making him feel. 

A groan from Black reminded Stretch that they weren’t alone. He broke away from the kiss gasping as Slim’s fingers stroked along his outer lips teasingly, and he heard Black laugh again when he opened his legs wider to give his double better access. Stretch wasn’t sure what came over him, but just agreeing to give up his control like this was more of a turn on than he could have ever anticipated. 

“Good Boys.” Black’s voice was smoother than silk, the only indication of him being affected by this display being the way his eye lights kept flicking back to Stretch’s dripping pussy. “Work Him Up Thoroughly Mutt, But I Don’t Want Either Of You Speaking Without Permission. Remember Dogs That Do As They’re Told Get Rewarded”

Before Stretch had the time to ask Black if he was serious Slim’s fingers were inside him. He had to bite his tongue to stop a string of curses spilling out, but he didn’t care. Despite his earlier reservations Stretch really wanted to do as he was told. He may have been questioning why his mind had changed so quickly, but something about being told he was a good boy made his pussy tighten around the invading fingers. That and he really didn’t mind the idea of being referred to as a dog either; his mind giving him flashes of degrading scenarios as his climax rapidly approached. 

Slim must have realised he was getting close; he thrust his fingers into Stretch harder until he was a whimpering mess before stopping quickly and pulling out. Stretch gasped in shock as he felt the build up quickly fading, leaving him in a frustrated puddle of his own magic. Black’s grin only widened when Slim’s fingers plunged back inside his abused pussy, especially because Stretch had been unable to hide his scream. He whined and clamped a hand over his mouth as he tried to find something else to focus on. It was obvious that they weren’t going to let him cum any time soon.

He couldn’t look at Black; his smug expression coupled with the way his skin tight pants were straining in the crotch area was just making his need worse. He knew Black was big enough to have been choking Slim earlier, but seeing his cock so obviously outlined made his pussy throb. Stretch tried to focus on Slim, shifting his now formed ass back against him in hopes of stimulating his double’s magic enough to distract him. But there wasn’t anything to press against bar the cold leather of his pants, something that made Stretch’s magic tense uncomfortably. Had he got so caught up in his own head that he had failed to turn on his partner at all?

As if reading his mind Black leaned in closer on the chair, making Stretch feel completely at his mercy even though they weren’t touching. “Mutt Won’t Form Anything Until I Tell Him To” Black said, his expression softening just enough to be reassuring. “He’s Enjoying This Just As Much As I Am. Speak Mutt.”

“i could cum just listening to his noises alone, if that’s what you wanted m’lord” Slim growled next to Stretch’s skull as he flicked a thumb across his neglected clit. 

“Good Boy. I Think That’s Enough For Now.” Black stood up from his chair and moved towards them both, making a show of grabbing the bulge in his crotch. “Get Him On All Fours”

Slim withdrew his fingers with a pop before manoeuvring Stretch into position. Any protest Stretch had about being handled like a doll died on his tongue when he came face to face with his smirking tormentor. If he had thought that Black’s stare was intense before, it was nothing compared to seeing it up close. Black ran a thumb across Stretch’s heated cheekbone, tracing the freckles that became more prominent when he was flushed before clashing their teeth together harshly. The semi-sweet gesture was short lived though, Black moved to kneel behind him before running a gloved finger across his pussy with a hiss. 

“Gods You’re Soaking, You Did A Thorough Job Mutt.” Black dragged the worn leather across Stretch’s pussy firmly, the delicious friction making it impossible for him not to moan. “Look At You, So Sensitive. I Bet You Can’t Wait To Have My Hard Cock Inside You Hmm? Speak”

“yes! fuc- ah!” Stretch was cut off as Black’s other hand gave him a quick swat to his ass, the delicious mix of pleasure and pain breaking his last piece of dignity. He knew Black was trying to get him to beg, and Stretch felt an overwhelming urge to please him. “please- ah! please i need your cock so bad i can’t think!” 

“Good Answer. I Knew All You Needed Was A Firm Hand, Brat” Black caressed Stretch’s hip soothingly after unzipping his pants and lining up. Black paused just outside of his entrance to address Slim who had obediently sat himself on Black’s chair to await further instruction. “I Want You To Watch Me Fuck Him, Pay Attention To His Face”

“m’lord?” Slim whimpered, his unquestioning obedience slipping slightly as his eyes flicked between the other two skeletons on the bed. It was clear he was struggling to hold back, his unformed magic starting to show through his shorts.

Black paused completely, and with the way Slim’s expression shifted before he nodded Stretch guessed that there had been some kind of non verbal agreement between them. He didn’t have time to guess though as Black’s thick cock started pressing at his entrance. With all the preparation Slim had done Black managed to hilt himself in one thrust with a loud groan. Stretch could feel his inner walls gripping Black’s cock hard as he was immediately put back onto the edge of climax. But he couldn’t cum. Stretch could writhe and scream all he wanted, but he knew there was no way he would be able to cum without Black’s permission now. 

Not that he wanted to finish soon; he couldn’t get enough of the way Black’s cock was pushing his magic to it’s limit with every slow thrust. Tears pooled at his sockets as Stretch stole a glance at his double. Slim seemed in an even more desperate state than he was, his hips rocking against the chair as instinct took over. But he wasn’t tearing his eyes away from Stretch’s face, just like Black had instructed. To say that this type of undivided attention was making Stretch feel hotter would have been an understatement. 

“Do You See His Expression Mutt?” Black thrust in deep before rolling his hips, hitting spots inside Stretch hard enough to make him cry out in ecstasy. “ Beautiful. This Is What You Look Like When I’m Fucking You Mutt, This Is Why I Can’t Keep My Hands Off You. Do You Understand?”

Stretch watched in awe as Slim’s entire skull flush vibrantly with magic as his brother’s words sunk in. Stretch knew it was more than just kinky sex between them, but he was beginning to understand just how deep Black and Slim’s bond really was. He probably would have felt incredibly moved about being included if he wasn’t distracted by Black’s cock twitching deep inside him. It seemed Black was finally feeling the effects of holding back, and that just made Stretch want to feel him loose some of that control even more. 

When Slim eventually did find his voice it was breaking with desperation.“i do. m’lord…i-i can’t- please” 

“I’m Going To Let Him Cum Soon” Black responded with a hiss as he started to thrust inside Stretch again. It was slow and deep and it was driving the less experienced skeleton insane. “Form Your Full Body And Touch Yourself Mutt. We’re Both Going To Reward You For Being Such A Good Puppy Very Soon” 

Black finished his sentence with a particularly hard thrust before picking up his speed, moving in and out of Stretch’s pussy like a machine. Stretch scrambled to find something to grip onto, but with on of Black’s hands using his spine as a counterbalance he had no choice but to go along with it. After being edged for so long Stretch was practically sobbing, any efforts to keep his pride intact completely forgotten. If this was what Black meant by breaking him, he’d happily be broken every fucking day. 

Black kept slowed his thrusts slightly so he could bring Stretch flush up against him, leaning up to lick the side of his skull. “Your Pussy Is Gripping Me So Hard, Slut. Are You Close?” Black’s tone had shifted into something guttural as he neared the edge himself. 

Stretch could cum just listening to him if Black would let him. He tried to respond, but he just babbled nonsense as his body screamed for release. 

Black gripped him hard, punctuating each word with a deep thrust. “Ask. Nicely.” 

It dawned on Stretch that he wasn’t going to get to cum unless he gave Black what he wanted.“s-sir please, i want to feel you fill me up, i need your cock!” He could barely believe the words that were leaving his mouth but Black’s animalistic growl told him all he needed to know. “fuck, fuck! i’m so close! oh gods please sir!”

Black thrust deeper as he moaned loudly, clearly getting close himself. At just the right moment he moved a hand to Stretch’s neglected clit to make him see stars. “You Want My Cum Huh? Such A Dirty Brat. Cum For Me Papy. Milk Me Fucking Dry” 

Stretch’s orgasm hit him hard, the dirty talk coupled with the rough treatment making him scream Black’s name as his whole body started to convulse. Black cursed under his breath before cumming himself, filling Stretch up to the brim with magic. He pulled out quickly though and Stretch was dazed for a second before his eyes fell back onto Slim. He had done exactly as he was told, naked and with a full ecto-body it was easy to tell how much he had enjoyed the show. Slim currently had three fingers inside himself and was visibly shaking with the effort of holding back. Black only needed to nudge Stretch in the right direction to have him eagerly crawl onto the floor towards his double. 

Black had mentioned about rewarding him for being a good boy after all. 

The moment Stretch tasted the musky tang of magic he was moaning into Slim’s pussy, replacing the fingers inside with his own. He may have just had one of the most intense orgasms of his life, but it had been like breaking a damn on his self control. He wanted more, and he was so eager to please them both. Black had followed him over to where Slim was sat, pausing to pet his skull softly before going to stand behind his brother. He was leant against his skull and whispering all kinds of filth as his fingers twirled and pulled at Slim’s over-sensitive nipples. Stretch had only messed around with forming a pair of breasts a few times in the past himself. But seeing his counterpart writhe as Black handled them roughly he hoped he would get the opportunity to experiment with his own in the near future. 

Slim’s eyes had been lidded and heavy as he enjoyed both of their attentions, but something Black had said had made him look at Stretch dead in the eyes. It was almost like he was pleading with him, and Stretch realised he’d finally been given permission to cum as well. Doubling his efforts Stretch licked a long stripe up his double’s pussy, curled his fingers, and then rolled Slim’s clit into his mouth. He tentatively added a little pressure to his teeth, knowing just how good that edge of pain was for him and how similar they seemed to respond. Slim arched in a silent scream and Stretch felt his mouth being filled with magic in spurts that he swallowed greedily. 

He rode Slim through his climax, teasing and licking up everything his double had to offer. As well as wanting Slim to enjoy himself fully, Stretch realised that he really didn’t want this to end. His magic was still summoned and he could feel the way it was still throbbing from their earlier antics. He drew back from Slim only to have Black push his head back down forcibly. Stretch wasn’t sure how Black had managed to slip behind him again, but he groaned loudly into his double when he felt gloved hands tracing up his dripping lips again.

“I Didn’t Give You Permission To Stop” Black clicked his tongue before using his other hand to spank Stretch’s ass.

Stretch cried out in pain before arching his back as he felt the gloved hand enter him. Black hissed at his reaction, taking his time to slowly push inside before circling a thumb around Stretch’s other hole. 

“You Didn’t Think We Were Done, Did You?”


End file.
